Introduction Flea biology Fleas

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5.2.1. Rodent fleas

Much of what is known about fleas is based on the biology of rodent fleas, especially Xenopsylla spp. on domestic rodents and Oropsylla montana and other flea species on ground squirrels Metzger Rust, 2002. Rodent fleas have been the subject of intense biological investigation Gage Kosoy, 2005 because they are the vectors of the causa- tive agents of two significant human diseases, bubonic plague and murine typhus. Most rodent fleas are nest fleas, moving onto the host only to feed.

5.2.2. Cat fleas

The cat flea Ctenocephalides felis is not considered a major threat to human health because, as it is rarely found on rodents, it usually has little chance to transmit disease agents from rodent reservoirs to humans. Also, it has been shown to be an inefficient vec- tor of plague Pollitzer, 1954. It does, however, produce significant discomfort, due to a pruritic reaction to salivary secretions, both in human beings and in other animals. The cat flea is a serious urban pest, infesting pets, such as dogs and cats, as well as urban wildlife, such as the northern raccoon Procyon lotor, the Virginia opossum Didelphis virginiana , the striped skunk Mephitis mephitis, foxes Vulpes spp. and coyotes Canis latrans Rust Dryden, 1997. In urban settings, these wild animals, as well as feral cats and dogs, maintain cat flea populations and build a natural reservoir for reinfestation of domestic pets. Even homes without a pet can experience severe cat flea problems, if wild or feral animals nest in the crawl space or attic and share their fleas. Typically, migrant animals den under the structure in the spring; once the young leave the nest, it is aban- doned, and the fleas left behind climb up through subflooring, avidly seeking a blood- meal from any warm-blooded host.

5.2.3. Flea development

Because rodent fleas and cat fleas share many similarities in their life-cycles, the cat flea will be used to provide an overview of flea development. Differences between them are provided to distinguish the two. The eggs of cat fleas are oval, measuring 0.5 mm in length, with tiny openings called aeropyles in one end of their white shells. A female cat flea produces about one egg an hour while she remains on the host. The smooth eggs are not sticky, so they easily sift through the host’s pelage to collect in the surrounding environment, concentrating in areas where the host spends the most time. Cat flea eggs hatch in 1–10 days, depending on temperature and humidity Dryden Rust, 1994. The majority of eggs hatch within 36 hours at 70 relative humidity and 35°C, while at 13°C most of the eggs hatch within six days Silverman, Rust Reierson, 1981. Flea larvae are white, legless, eyeless maggot-like creatures, covered sparsely with hairs. A neonate is scarcely larger than the egg from which it emerged, while full-grown lar- vae are about 5 mm long. Larvae live off the host, feeding on organic debris and adult Fleas 156

5.1. Introduction

While over 2200 species of fleas are known worldwide, most of them are of no public health significance and do not have an impact on people or their companion animals, because they are found only on specific wild hosts. Of primary health and veterinary concern are rodent fleas, especially Xenopsylla spp., and fleas found on companion ani- mals, Ctenocephalides spp.. While other flea species, such as L eptopsylla segnis the European mouse flea, are found on peridomestic animals, they are considered unlikely vectors Pratt Wiseman, 1962. Both Xenopsylla spp. and Ctenocephalides spp. have worldwide distribution.

5.2. Flea biology

Fleas have developed two host-mainte- nance strategies. Host fleas remain on the host, exhibiting strong fidelity to the ver- tebrate, once a host is acquired, and aban- doning their vertebrate host only when it dies. The host provides food as blood, warmth and shelter, giving the flea little incentive to leave the host, especially since there is no guarantee of it acquiring ano- ther host. T he flea’s need to frequently feed increases its inclination to remain near the host Fig. 5.1. In contrast, nidi- colous fleas remain in the nest, moving to the host only to feed Krasnov, Khokhlova Shenbrot, 2004. N est fleas parasitize animals such as rodents that return to the nest daily, ensuring that the flea will be able to obtain regular blood-meals. Typically, nest fleas are poor jumpers, moving primarily by crawling, while host fleas have well-developed jumping legs. While the adult flea is dependent on the vertebrate host, flea larvae live off the host. Nevertheless, they also depend on host blood, in the form of adult flea faeces, for nutri- tion. Adult fleas ingest much more host blood than they need or can utilize for their own nutrition; thus, adult flea faeces are often described as being partially digested or undi- gested host blood Rust Dryden, 1997. Rodent and cat flea species have similar holo- metabolous life cycles, with free-living larval stages undergoing complete metamorpho- sis, resulting in the parasitic host-dependent adult stage. Fig 5.1. Adult fleas feed exclusively on blood Source: Photo by N.C. Hinkle. Public Health Significance of Urban Pests 159

5.3. Health risk and exposure assessment